Presence of antibodies against cyclic citrullinated peptides in patients with 'rhupus': a cross-sectional study

Abstract

'Rhupus' is a rare condition sharing features of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). If rhupus is a distinctive entity, an overlap between RA and SLE or a subset of SLE is currently debated. This study was performed to explore the prevalence of antibodies against cyclic citrullinated peptides (anti-CCP antibodies) in rhupus. Patients meeting American College of Rheumatology criteria for RA, SLE, or both were included. Clinical and radiographic features were recorded and sera were searched for anti-CCP antibodies, rheumatoid factor, antinuclear antibodies, anti-extractable nuclear antigens, and antibodies against double-stranded DNA (anti-dsDNA antibodies). Seven patients for each group were included. Clinical and serological features for RA or SLE were similar between rhupus and RA patients, and between rhupus and SLE patients, respectively. Values for anti-CCP antibodies obtained were significantly (p < 0.05) higher in RA (6/7) and rhupus (4/7) than in SLE patients (0/7) and healthy subjects (0/7). Our data support the possibility that rhupus is an overlap between RA and SLE, because highly specific autoantibodies for RA (anti-CCP) and for SLE (anti-dsDNA and anti-Sm) are detected in coexistence.

Figure 1

Analysis of serum anti-CCP antibodies. Patients with rhupus and those with rheumatoid arthritis (RA) had significantly higher serum antibodies against cyclic citrullinated peptides (anti-CCP antibodies) than patients with systemic lupus erythematosus (SLE) and healthy subjects (*p < 0.05). Results are expressed in U/ml for each patient. Horizontal lines indicate the median value for anti-CCP antibodies in each group. The dotted line represents the cutoff value for positivity (60 U/ml).